1. Field of the Invention
This invention relates generally to high-pressure blowout preventer testing in subsea environments, and more particularly to a telescoping multi-gage blowout preventer test tool and method for testing different size ram and annular BOP's, or choke and kill lines in one trip.
2. Brief Description of the Prior Art
Blowout preventer or BOP stacks are connected to oil and gas wellheads on the sea floor for controlling the wellhead during drilling rig operations. The blowout preventer stack will usually include several blowout preventers of various types which are capable of closing in the wellhead in the event of excessive pressures downhole. For example, a typical blowout preventer stack may include several ram-type blowout preventers (blind-ram and/or variable ram), and one or more annular blowout preventers connected above the ram-type blowout preventers. A riser pipe connected to the uppermost blowout preventer extends to the drilling rig at the surface.
Typically subsea wellheads use a tapered drill string system wherein a larger diameter drill string is used for drilling an initial portion of the well, and successively smaller diameter drill strings for drilling the lower portions of the well. Thus, the blowout preventer system must be capable, for example, of sealing off the annular space surrounding 51/2" and/or 5" O.D. pipe and also 31/2" O.D. drill pipe.
Testing of the blowout preventer stack is typically accomplished by connecting a test plug to a length of drill pipe of the diameter to be tested, running it into the wellhead such that the test plug seals in the wellhead, and then testing the blowout preventer system for that particular size of drill pipe. The first drill string and test plug is retrieved from the wellhead, and the process is repeated for each size of drill pipe used in the system.
This repetitive tripping or running and retrieving the test drill string to test against each of the different size drill pipes requires excessive time, labor, and expense, particularly in subsea wellheads which may be several thousand feet below the drilling platform.
There are several patents which disclose various blowout preventer testing apparatus and methods.
Crain, U.S. Pat. No. 4,347,733 discloses a blowout preventer test system utilizing a pipe nipple threaded at both ends and having a central bore through which fluid is conveyed. A reduced orifice at the central portion of the bore constricts fluid flow through the bore. The nipple has instrumentation taps through its side wall for attaching a differential pressure recording device.
Hynes et al, U.S. Pat. No. 4,554,976 discloses a blowout preventer test tool having an upper body and lower sealing body releasably connected by left-hand threads, and a check valve landed in the bore of the tool to prevent downward flow of fluid but allow upward flow and the attached drill pipe for detecting leaks of the sealing tool during pressure testing. During testing of a shear ram blowout preventer, the upper body is disconnected from the lower body by turning the drill pipe to the right. Raising the drill pipe then causes the upper body to shift a set of right-hand threads into position and move the upper body and drill pipe above the shear ram BOP allowing it to be closed for pressure testing.
Stockinger et al, U.S. Pat. No. 4,881,598 discloses a blowout preventer testing apparatus designed to close a smaller drill string pipe and a larger drill string pipe. The apparatus includes a first elongated cylindrical testing mandrel having an O.D. of the smaller drill pipe telescopingly received inside of a second elongated cylindrical testing mandrel having an O.D. of the larger drill pipe. The mandrels are releasably locked together in an extended position for testing against the first mandrel, and released to a collapsed position for testing against the second mandrel without tripping the apparatus out of the wellhead.
The present invention is distinguished over the prior art in general, and these patents in particular by a multi-gage blowout preventer test tool for testing different size ram and annular BOP's in one trip. The present tool has an outer test tube assembly and an inner tube assembly connected in telescoping relation. The exterior of the outer test tube assembly has a plurality of pipe gage diameters corresponding to different drill pipe sizes. A top sub at the top end of the outer tube assembly connects to the drill string and contains an upper seal assembly and stinger. The bottom end of the inner tube assembly is secured to a bottom sub and the bottom end of the outer tube assembly is releasably connected to the bottom sub in the collapsed position. The bottom sub is connected to a test plug and tail pipe assembly and the tool is lowered through the riser pipe and BOP stack to set the test plug in the wellhead. A wireline retrievable dart is sealingly engaged in the upper seal assembly and drilling fluid flow bypasses the upper seal assembly through fluid passageways between the inner and outer tube assemblies and is vented through relief ports at the lower end of the tool. Ram and annular BOPs are tested against a first set of the pipe gage diameters with the tool in its collapsed condition, and then the outer tube assembly is uncoupled from the bottom sub and lifted to its extended position such that another set of the pipe gage diameters are positioned within the BOP stack and the rams and annular BOPs are then tested against the second axially positioned set of corresponding pipe gage diameters.